This invention relates to a circular knitting machine, and particularly to a double-cylinder knitting machine equipped with a safety device for opening the latches of the needles being transferred from one needle cylinder to the other.
As known in the art, on transferring a double-hooked needle in a double-cylinder circular knitting machine, e.g. when the needle is required to convert from plain stitch knitting over to purl stitch knitting, it is requisite of the needle to present its latch in the opened state, such that the appropriate hook of the slider intended to pick up the needle being transferred is enabled to insert itself into the space enclosed by the needle hook and engage said hook, preparatory to pulling the needle within the respective needle cylinder. At this stage, the slider also effects a swinging movement, projecting for a moment with its end out of the cylinder groove and then swings back to hook up the needle to be transferred.
If the latch is closed, it happens that, when the slider swings back to hook up the needle, it meets opposition to its hook by the closed latch, distorts the latter, and since the slider is urged to swing back by specially provided cams, breaks the latch and is itself damaged.
In order to prevent such occurrences, the cams located upstream of the transfer area are configurated such as to bring the slider and needle close to each other at the precise point where the closed latch approaches the needle hook, such that during the subsequent relative movement of the needle and slider the latter first inserts itself with its tip between the latch and the needle hook, and then gradually opens up the latch.
Such a system, however, requires that all the needles to be transferred be correctly brought to an accurate encounter with the slider, as explained above.
On the machines designed for a more complex operation, e.g. on circular knitting machines provided for "links-Jacquard" knitting, wherein two or three feeds are provided having different color threads and purl stitch operation is contemplated and various pattern drums are to be pre-arranged, it even more easily occurs, consequently to a mistake in the presetting of one of the pattern drums, that the needle to be transferred performs a wrong movement, thereby it reaches the transfer point with the latch in the non-opened state.
Assuming, for instance, the case of a "links-Jacquard" knitting machine, wherein the needles not involved in knitting at the feed located after the transfer area (considering the needle direction of movement with respect to the cams) must remain in a "floating" or low position, whereas both the needles which are to be operative at that feed and the needles which are to be transferred must follow a higher track. Now, if a needle to be transferred, rather than following the high track is erroneously brought by its slider to follow the "floating" track, then it will be raised anyhow to a transfer position by its pertinent underlying selecting jack, but will reach the height level for hooking up the slider of the other needle cylinder when this slider is swung out of its cylinder groove and thus is unable to open the needle latch, should the latter have stayed closed. In this case, the aforementioned events would occur, i.e. the breaking of the needle and slider as the latter swings back into the groove.
However, the correct arrangement of the pattern drums, that is the correct arrangement on such drums of the various so-called safety teeth or pins, which are operative to direct along the right track the sliders and needles associated therewith, is susceptible of errors that are greater the more complicated the knitting is. The absence of even a single tooth or pin arranged to bring the needle to be transferred to a position suitable for the opening of the latch is enough not only to result in a faulty product but also to break the slider and needle, thereby the machine must be stopped, the error on the drum located, the drum reassembled and the slider and needle replaced, thus causing considerable delay and loss of production.